A number of systems and programs are offered on the market for the design, the engineering and the manufacturing of objects. CAD is an acronym for Computer-Aided Design, e.g. it relates to software solutions for designing an object. CAE is an acronym for Computer-Aided Engineering, e.g. it relates to software solutions for simulating the physical behavior of a future product. CAM is an acronym for Computer-Aided Manufacturing, e.g. it relates to software solutions for defining manufacturing processes and operations. In such computer-aided design systems, the graphical user interface plays an important role as regards the efficiency of the technique. These techniques may be embedded within Product Lifecycle Management (PLM) systems. PLM refers to a business strategy that helps companies to share product data, apply common processes, and leverage corporate knowledge for the development of products from conception to the end of their life, across the concept of extended enterprise. The PLM solutions provided by Dassault Systèmes (under the trademarks CATIA, ENOVIA and DELMIA) provide an Engineering Hub, which organizes product engineering knowledge, a Manufacturing Hub, which manages manufacturing engineering knowledge, and an Enterprise Hub which enables enterprise integrations and connections into both the Engineering and Manufacturing Hubs. All together the system delivers an open object model linking products, processes, resources to enable dynamic, knowledge-based product creation and decision support that drives optimized product definition, manufacturing preparation, production and service.
Light transport simulation is an important component of realistic image synthesis. The body of research work related to this phenomenon is referred as “global illumination” and, despite its well-known physics laws, remains a challenging problem due to its high computational cost, with even more critical consequences for real-time scenarios. Hidden behind the recursive nature of the rendering equation as discussed in KAJIYA, J. T. 1986. The rendering equation. In ACM Siggraph Computer Graphics, vol. 20, ACM, 143-150, global illumination simulation has been addressed in a large number of approaches, for the high degree of realism it brings to special effects, previsualization, animated movie production and video games.
Currently, two lines of research can be distinguished. The first one is “interactive rendering” which aims at quickly providing a visually convincing approximation of global illumination. The second one is “offline rendering” which targets a solution which is as close as possible to physics.
Among the various strategies that can be used to achieve real-time performance for “interactive rendering”, exploiting the low frequency behavior of distant incoming radiance has proven to be effective. For instance, hierarchical radiance caching methods discussed in WALTER, B., FERNANDEZ, S., ARBREE, A., BALA, K., DONIKIAN, M., AND GREENBERG, D. P. 2005. Lightcuts: a scalable approach to illumination. In ACM Transactions on Graphics (TOG), vol. 24, ACM, 1098-1107 exploit this property by computing a tree over the geometry of the scene, which stores a multiscale radiance function. Assuming indirect lighting being modelled by virtual point lights (VPLs) located on the scene surfaces, every internal node of this tree provides a representative radiance response of its related subtree and is used as a substitute to it as soon as the radiance is evaluated from a distant location. The set of nodes used to evaluate the incoming radiance at a given point (e.g. unprojected image pixel) is called a light cut, since gathering a node induces discarding its children.
A number of high-performance implementations of light cut gathering processes have been proposed, but most of them rely on precomputing and maintaining the tree, which can have a significant memory and computational cost.
Mittring et al. (MITTRING, M. 2007. Finding next gen: Cryengine 2. In ACM SIGGRAPH 2007 courses, ACM, 97-121) introduced an ambient occlusion approximation method using the depth-buffer as an economic, random-accessible substitute to the actual (potentially large) geometry of the scene, and parameterizing the light cache in screen-space. A large variety of other methods exploits screen-space approximations to lower the computational complexity of some lighting effects. However, despite their real-time and dynamic performances, such approaches rely on depth peeling and multiple views rendering to account for the full geometry of the scene i.e., beyond the first depth layer and outside the view frustum, which quickly impacts negatively their native speed.
In contrast to screen-space approaches, solving for indirect illumination in object-space avoids such view-dependent artifacts, at the cost of less GPU-friendly light caches. For instance, Instant Radiosity (IR) methods as discussed in KELLER, A. 1997. Instant radiosity. In Proceedings of the 24th annual conference on Computer graphics and interactive techniques, ACM Press/Addison-Wesley Publishing Co., 49-56 work with a set of secondary point light sources, called Virtual Point Lights (or VPLs), directly generated on the geometry illuminated by the primary sources. Thus, a VPLs set acts as a discrete representation of the scene's indirect lighting and allows to reduce computations drastically when approximating light bounces. However, scaling up to massive data requires huge amounts of VPLs. This is challenging as both generation and shading costs of so many VPLs is prohibitive in dynamic scenes.
Finally, the Deep Screen Space (DSS) approach discussed in NALBACH, O., RITSCHEL, T, AND SEIDEL, H.-P. 2014. Deep screen space. In Proceedings of the 18th meeting of the ACM SIGGRAPH Symposium on Interactive 3D Graphics and Games, ACM, 79-86. 2014 proposes to exploit the advantages of both screen-space and object-space radiance caching. The same way as object-space strategies, this method generates on-surface VPLs, even on occluded geometry that may still impact the image; and similarly to screen-space approaches, it benefits from a native GPU support, with the tessellator unit—instead of the rasterizer—being used as a surface sampler to generate the VPLs. Still, although DSS can successfully be used for rendering small to medium size scenes, it cannot cope with larger ones, where the real-time constraints imposes decimating geometry rather than refining it.
Within this context, there is still a need for an improved method rendering the global illumination of a three-dimensional scene.